34.1 WHAT IS SIX SIGMA?

Six Sigma Versus Other Quality Initiatives. Quality and yield problems arise fundamentally from two causes critical dimension variations and contamination. By reducing the process variation, the cost of poor quality decreases and profitability increases.

Six Sigma is, basically, a quality objective. It is an organization-wide, leadership-driven, process-oriented initiative, designed so that processes produce no more than 3.4 defects per million opportunities (DPMO). To achieve this, a relentless pursuit of variation reduction in all critical processes needs to be carried out. Processes are required to operate so that the engineering specifications are at least plus or minus Six Sigma (sigma stands for standard deviation) from the process target.

The Six Sigma initiative has contributed to a change in the discussion of quality from one where defects were measured in percentages to a discussion of defects per million. It emphasizes setting extremely high objectives. Goals are stretched to focus people on process improvements. With the knowledge that more than 200 process steps are usually necessary to manufacture a chip, old ideas about satisfactory quality levels are no longer acceptable. With shrinking dimensions, semiconductor yields will become increasingly sensitive to manufacturing variations.

Six Sigma brings together problem-solving tools that are already known (such as gauge repeatability and reproducibility studies, flow charts, capability analysis, control charts, probability distributions, and design of experiments) into a methodology that enables people to improve their processes. The Six Sigma...